Sediment Oxygen Demand(SOD) is a key parameter for water quality analysis and for water quality modeling in rivers,lakes,estuaries and bays.The SOD can be measured both in the laboratory and in situ.However,the in situ technique appears to be the better approach for measuring SOD,as it likely to provide more representative and accurate results.In order to optimize the design of in situ SOD measurement chambers,the three-dimensional flow fields in cylindrical SOD measurement chambers, commonly used for in situ measurements,have been numerically simulated by using the RNG-based k-s double equation turbulence model.SOD chambers with three different inflow pipe configurations were investigated.The results show that chamberⅢpresents distinct advantages over the other designs for in situ SOD measurement,because good flow mixing can be achieved and bottom sediment suspension can be avoided in the chamber.The numerical simulation results were validated by comparison with existing results derived from laboratory experiments.The SOD measurement chamber designed to reflect the results of the numerical simulations was successfully tested for in situ SOD measurements in both fresh and saline waters. Sediment Oxygen Demand (SOD) is a key parameter for water quality analysis and for water quality modeling in rivers, lakes, estuaries and bays. The SOD can be measured both in the laboratory and in situ. However, the in situ technique appears to be the better approach for measuring SOD, as it likely to provide more representative and accurate results. In order to optimize the design of in situ situimetric measurement chambers, the three-dimensional flow fields in cylindrical SOD measurement chambers, commonly used for in situ measurements, have been numerically simulated by using the RNG-based ks double equation turbulence model. SOD chambers with three different inflow pipe configurations were investigated. The results show that chamber IIIpresents distinct advantages over the other designs for in situ situometry, because good flow mixing can be achieved and bottom sediment suspension can be avoided in the chamber. numerical simulation results were validated by comparison with existing results der ived from laboratory experiments. The SOD measurement chamber designed to reflect the results of the numerical simulations was successfully tested for in situ SOD measurements in both fresh and saline waters.